It started happening yesterday after the 7pm update and only happens on some sites. Oddly I have two identical ones on the same network and it occurs on one but not the other. (On iOS it made my editor white out and I had to disable the visual editor entirely). So it looks like it's not initializing at all for iOS. I think it's not activitating TinyMCE since the OP (see the forum link) was getting oddly formatted HTML in his text editor.

I know the visual editor was working earlier because I had to switch to it in order to insert images, but now I'm 'stuck'.

Got the error on Chrome, iOS Safari, and I'll test more when I get to a grown up computer.

One site: I can switch to it, but my page it blank white (no content shows) and I can't get BACK. In the end, I made a new post, inserted media (nothing shows), saved, and THEN I could go back to text editor. If I go back to visual editor, the cycle starts again.

I managed to reproduce it on a clean site... With SEOSlides (of course I did the 'install the plugins that are different' method). o.O I would be surprised to find that's a plugin we have in common, but I have asked.

Not sure this is a broken plugin issue or a tinymce4 is a dingus issue or ... what. Will report upstream to SEOSlides too :)

Worst part is that the errors are inconsistent. Is it possible that all these errors are from stale browser cache? We are not refreshing $wp-version on each script or style change like ​bumpbot used to do. Perhaps would need to do that manually from time to time to make sure we bust the caches.

I can reliably reproduce the no-content/no-visualeditor if I use SEO Slides, but I tried the list of plugins from the forum OP and couldn't break it. So something's clearly kicking JS in the underpants.

The icons thing I flushed my caches the hard way (full form delete from browser AND server) and now it's okay. So yeah, caching. I have SCRIPT_DEBUG on, but that doesn't force the version. Maybe each 'nightly' should bump with the date? I mean, we're on trunk, we should know :)

Out of curiosity, is there documentation anywhere for how plugin devs can update their code to work with the newer APIs? (i.e. Not depend on method stubs in core but to actually do things the right way?)